.TH MT 1
.SH NAME
mt \- magnetic tape control
.SH SYNOPSIS
.B mt
.RB [ \-f
.IR device ]
.RI [ count ]
.SH DESCRIPTION
.B Mt
is a user interface to the magnetic tape commands described in
.BR mtio (4).
It allows one to space a tape forwards or backwards, write end of file
markers, etc.
.PP
With the
.B \-f
option a tape device can be named, otherwise the environment variable
.B TAPE
is used if set, otherwise the default device
.B /dev/nrst4
is assumed.  Standard input is used if the tape name is a dash (\-).  The
.I count
argument is used to tell how many blocks or files to space or how many file
markers to write.  It may be a C-style decimal, octal or hexadecimal constant,
by default "1".
.PP
.I Command
is the action to perform, it may be one of the following, or any
unambiguous prefix (like
.B st
for
.BR status ):
.TP 15
.B eof, weof
Write
.I count
end-of-file markers.
.TP
.B fsf
Forward space
.I count
file markers.
.TP
.B fsr
Forward space
.I count
records.  (The size of a record depends on the tape, and may even be
variable, depending on the size of the writes.)
.TP
.B bsf
Backwards space
.I count
files.  The count may be zero to backspace to the start of the current file.
(A tape device need not support backwards movement, or may be very slow
doing it.  Rewinding and forward spacing may be better.)
.TP
.B bsr
Backwards space
.I count
records.  The tape is positioned after the last block of the previous file
if you hit a filemark when spacing backwards.  The block count is set to -1
to indicate that the driver has no idea where it is on the previous file.
.TP
.B eom
Forward space to the end of media.
.TP
.B rewind
Rewind the tape.
.TP
.B offline, rewoffl
Rewind and take offline.  This may cause some drives to eject the tape.
.TP
.B status
Shows the status of the drive, the sense key of the last SCSI error,
current file number, current record number, residual count if the last
command that encountered end-of-file, and the current block size.
.TP
.B retension
Removes tape tension by winding and rewinding the tape completely.
.TP
.B erase
Erases the tape completely and rewinds it.
.TP
.B density
Sets the density code to read or write the tape to
.IR count .
Density codes supported depend on the drive.  This command need not be
used if the drive senses the proper density on read and can only write
one density.
.TP
.B blksize, blocksize
Sets the block size used to read or write the tape to
.IR count .
This command may be used to select a fixed block size for a variable block
size tape.  This will speed up I/O for small block sizes.  Use a zero
.I count
to use variable sized blocks again.
.SH ENVIRONMENT
.TP 15n
.B TAPE
Tape drive to use if set.
.SH FILES
.TP 15n
.B /dev/nrst4
Default tape device.
.SH "SEE ALSO"
.BR mtio (4),
.BR st (4).
.SH AUTHOR
Kees J. Bot (kjb@cs.vu.nl)
